Generally, in image forming apparatuses such as laser printers, developer cartridges containing toner are detachably attached to their apparatus bodies. For example, JP-A-2006-267994 discloses an image forming apparatus capable of determining whether the attached developer cartridge is a new product (new-product detection) and also determining type of the developer cartridge (type detection) (see JP-A-2006-267994).
Specifically, the image forming apparatus disclosed in JP-A-2006-267994 includes, in a main unit, a swingable arm-shaped actuator, a spring that urges the actuator to a neutral position, a sensor that detects a swing of the actuator, and a controller that carries out new-product detection and type detection based on signals from the sensor. In addition, the image forming apparatus includes, in the developer cartridge, one or two contact projections extending radially outside from a predetermined shaft portion and a sensing gear that rotates around the shaft portion integrally with the contact projection.
In this image forming apparatus, when the developer cartridge is attached to the main unit, the contact projection presses one end of the actuator to swing the actuator, and this swing is detected by the sensor. A signal detected by this sensor is sent to the controller as a first detection signal. The controller determines, if having received this first detection signal, that the developer cartridge is a new product.
Moreover, in this image forming apparatus, when, for example, a front cover is closed after the developer cartridge is attached, a warm-up operation (idle rotation operation) is executed by the controller. Here, the idle rotation operation means an operation to rotate an agitator in the cartridge in order to agitate the toner contained in the developer cartridge.
In such an idle rotation operation, a transmission force from a drive source provided in the main unit is transmitted to the agitator and the sensing gear on the developer cartridge side via a plurality of gears. Thereby, agitation of the toner by the agitator is started, and the contact projection is rotated to further press the end of the actuator and separates from the actuator at a predetermined position. Thereafter, the actuator is to return to the neutral position due to an urging force of the spring. At this time, when two contact projections exist, the second contact projection again presses the end of the actuator to swing the actuator, and this swing is detected by the sensor. A signal detected by this sensor is sent to the controller as a second detection signal.
When the controller receives the second detection signal, the controller determines that the developer cartridge has a type A (for example, a type where the maximum sheets to be printed are 6000). Meanwhile, when the controller does not receive the second detection signal, the controller determines that the developer cartridge has a type B (for example, a type where the maximum sheets to be printed are 3000) different from the type A.
However, in the above image forming apparatus, the type have been detected based on the number of times the contact projection contacts with the actuator. Therefore, in order to make the two contact projections contact with the actuator, it is necessary to increase the amount of rotation of the sensing gear. For this reason, the moving range of the contact projections is increased. In addition, for the necessity of providing other elements outside the moving range thus increased, the size of the developer cartridge cannot be reduced.